There have been numerous reports in the past two weeks about the four former NFLstars — Tony Dorsett, Joe DeLamielleure, Leonard Marshall and Mark Duper — diagnosed with early signs of a brain condition called chronic traumatic encephalopathy, or CTE.

These reports have shifted into discussions on how to prevent other players from developing CTE, including possible changes to game rules, special testing and delaying youth involvement.

But, what exactly is CTE?

CTE is a condition where repeated blows to the head or neck — in contact sports such as boxing, football and hockey — eventually lead to long-term brain damage. The head trauma can be as simple as hitting the ground during a tackle or a full speed helmet-to-helmet collision.

In CTE, the brain breaks down and develops a build-up of an abnormal protein called tau, which contributes to the symptoms.

What CTE looks like

The symptoms include cognitive deficits such as memory loss, impaired judgment and confusion; behavioral changes such as impulse control or aggression; and psychiatric symptoms such asdepression, paranoia and suicide. Eventually, the degeneration of the brain in CTE causes dementia.

Dorsett appeared on ESPN last week and confirmed that he has memory deficits, emotional outbursts, depression and thoughts of suicide.

Typically, CTE can only be diagnosed postmortem during an autopsy, however, Dorsett and other athletes are showing early symptoms of the condition.

Just a concussion, or brain damage?

We now know that a concussion — including “seeing stars” or “getting your bell rung” — is, in fact, minor brain injury.

Concussions have been a part of the game — even as of last week, NFL teams reported a total of 62 concussions since the beginning of the 2013 season — but there’s an increased awareness lately. Simply put, any blow to the head or any impact that shakes the brain around with a resulting symptom — headache, nausea, vomiting, dizziness, memory loss or feeling foggy — is a concussion.

Making this definition more accurate has become important in identifying who is actually at risk for long-term damage. But, while CTE is known to come from repeated concussions, it can also occur in players who take blows with seemingly no symptoms.

Advocates say that this makes a case that even small blows without a full concussion could still have long-term damaging effects.

Putting two and two together

This issue is not new. Back in 2005, researchers at the University of North Carolina at Chapel Hill sent surveys to more than 3,000 members of the NFL Retired Player’s Association and found a connection between repeated football concussions and dementia later in life. In fact, they found a 37 percent higher risk of Alzheimer’s dementia among those who responded. Some needed help from family members to complete the survey.

That same year, University of Pittsburgh researchers published findings of an autopsy on a former NFL player 12 years out of retirement. He reportedly had a mood disorder, problems with cognition and symptoms similar to someone with Parkinson’s disease.

Two years later, in response to these new findings, The Sports Legacy Institute was created in Boston with the goal of promoting awareness of brain injury in sports and studying the brains of deceased athletes. That same year, they received their first donation to the brain bank from the family of Chris Benoit — a champion professional wrestler who ended his life in a shocking double-murder suicide.

Some speculated that steroids were responsible, but SLI, along with Boston University researchers, performed forensic testing that showed signs of CTE.

CTE and suicide

Since then, several other professional athletes who have committed suicide were found to have damage consistent with CTE.

In the same year, NFL defensive back Andre Waters committed suicide at age 44, and the pathologist who performed his autopsy told the New York Times that Waters’ brain had degenerated into a brain of an 85-year-old man and that his brain had characteristics of Alzheimer’s patients.

Boston University researchers also found CTE in the brain of former Pro Bowl Safety Dave Duerson who, at 50, committed suicide with a gunshot to the chest. He left a note asking that his brain be donated to the Brain Bank.

The month before, former Atlanta Falcons safety Ray Easterling committed suicide at 62 and his autopsy showed signs of CTE.

More research and testing

The SLI, in particular, continues to receive brain donations, perform testing and advocate about CTE. In January 2013, they published findings in the journal Brainshowing that 68 of the brains from 85 subjects with a history of mild repetitive brain trauma had evidence of CTE.

Since CTE can only be definitively diagnosed postmortem, there is a need for earlier testing and research among living athletes — both active and retired.